Cannot populate @OneToMany when using Embeddables

[pantajoe]

Describe the bug

Hey there! First of all, thanks a lot for this very stable and intuitive TS ORM! ❤️

Since a couple of versions, an @Embeddable can have a @ManyToOne relationship through its parent. This works fine.

However, the inverse side that would use a @OneToMany collection cannot populate the user.

Stack trace

No stack trace since no error.

To Reproduce

Here is an example setup:

@Embeddable()
export class Address {
  constructor(street: string, city: string, country: Country) {
    this.street = street
    this.city = city
    this.country = country
  }

  @Property()
  street!: string

  @Property()
  city!: string

  @ManyToOne()
  country!: Country
}

@Entity()
export class Country {
  @PrimaryKey({ autoincrement: true })
  id!: number

  @Property()
  name!: string

  @OneToMany(() => User, (user) => (user as any).address_country)
  users = new Collection<User>(this)
}

@Entity()
export class User {
  @PrimaryKey({ autoincrement: true })
  id!: number

  @Property()
  name!: string

  @Embedded(() => Address)
  address!: Address
}

You can populate the country property from the side of the User, but you cannot populate the users collection from the Country's side.

Expected behavior

One should be able to populate the users collection also from the Country's side.

Additional context
Here is a test suite that explains everything in detail:

import { MikroORM } from '@mikro-orm/core'
import { SqliteDriver } from '@mikro-orm/sqlite'
import { Address } from './address'
import { Country } from './country'
import { User } from './user'

describe('Issue', () => {
  let orm: MikroORM

  beforeAll(async () => {
    orm = await MikroORM.init({
      entities: [User, Country, Address],
      dbName: ':memory:',
      driver: SqliteDriver,
      allowGlobalContext: true,
    })
    await orm.schema.createSchema()
  })

  afterEach(async () => {
    await orm.schema.clearDatabase()
  })

  afterAll(() => orm.close(true))

  beforeEach(async () => {
    const germany = orm.em.create(Country, { name: 'Germany' })
    orm.em.create(User, { name: 'John Doe', address: new Address('Main Street', 'Berlin', germany) })
    await orm.em.flush()
  })

  test('the country can be populated through the address of a user', async () => {
    const user = await orm.em.findOneOrFail(User, { name: 'John Doe' }, { populate: ['address.country'] })
    expect(user.address.country.name).toBe('Germany')
  })

  test('the users can be populated through the address of a country', async () => {
    const country = await orm.em.findOneOrFail(Country, { name: 'Germany' }, { populate: ['users'] })
    expect(country.users[0].name).toBe('John Doe') // ❌ this one fails
  })

  test('can init the user collection of a country', async () => {
    const country = await orm.em.findOneOrFail(Country, { name: 'Germany' })
    await country.users.init()
    expect(country.users.isInitialized()).toBe(true)
    expect(country.users[0].name).toBe('John Doe')
  })
})

Versions

Dependency	Version
node	16.15.1
typescript	4.9.5
mikro-orm	5.6.13
sqlite3	5.1.4

[B4nan]

This is not supported - you could tell by the need to cast things to any to be able to define this. You can't define inverse side of such relation because embedded entity does not have a primary key, hence it has no identity.

I'll keep this open as a feature request, as it could work for inlined mode. It is partially connected to #3887, the root cause is the same.

[pantajoe]

Thanks for you quick response! Yeah, that's what I figured. Wasn't sure whether to declare this issue as a feature request or a bug.